Pitch control and feathering mechanism for variable pitch propellers



Sept. 23,1952 L. HAWORTH ETAL PITCH CONTROL AND FEATHERING MECHANISM FOR VARIABLE PITCH PROPELLERS Filed Jan. 19, 1950 m vEmToas. HBwoa-m Q, a. Jag-(amen) am PM The pumps 20, 24 are engine-driven, the drives being indicated diagrammatically at 29, respectively.

The constant speed governor unit as illustrated is of known construction and comprises a centrifugal governor 3| driven from the engine through a drive indicated at 32 and arranged to adjust a piston valve 33 working in a cylinder 34 against spring 39. The piston valve 33 controls the flow of pressure fluid from a pump 35 to the hydraulic motor l5, the return fluid passing to the suction side of the pump 35 so that the governor hydraulic circuit isa circulatory circuit. This circuit comprises pump 35 which delivers fluid into pipe-line 31 past non-return valve 39 to the cylinder 34 and thus, according to whether the piston valve 33 is raised or lowered (as viewed in the drawing) from its central position, to the upper side l5c or lower side l5biof the hy-. draulic motor piston [5a. When pressure fluid is admitted to the space I50, the piston 15a snovesz downwardly (as viewed in the drawing) and the pitch of the blades is coarsened. When pressure fluid is admitted to space l5b, the pitch of the blades [4a is fined-off. The return fluid flowsfrom space I50 or [5b past valve 33 into pipe-line 38 back to the suction side of pump 35. A relief, valve 40 is provided between pipe-line 31 downstream of valve 36 and pipe-line 38. The

fluid flow in the governing operation is indicated by arrows 43.

The spring 39 against which the governor 3| acts to lift the piston valve on increase of engine speed has an abutment 4| which is adjustable by means of lever 42 through rack and pinion 44 to select the rotational speed to which the airscrew is governed. As illustrated, on increase of speed from the selected speed, the piston valve 33 is raised admitting pressure fluid to the space 150 to coarsen the airscrew blade pitch, and on decrease of speed from the selected speed, the piston valve 33 is lowered admitting pressure fluid to the space l5b to fine off the airscrew blade pitch.

Any loss of pressure fluid from the governor circuit is made up from the engine oil circuit through a branch pipe line 45 connected at one end to pipe-line 2| between filter 22 and valve 23 .and at its other end to pipe-line 38. The toppingup oil flow is indicated by arrow 46.

The feathering and unfeathering unit is normally employed to feather the airscrew blades No, that is to move them to maximum coarse pitch, when the engine fails or is intentionally stopped in flight of the aircraft and to move them from the feathered position on restarting the'engine. The unit comprises in the form illustrated a pump 41 driven by a compound wound D. C. motor 48 so as to be independent of the engine for its operation. The pump draws oil from the 4 lever 51 is moved to lift the valve and the switch 54 is closed. At the end of the feathering operation the switch 54 may be opened to avoid continuous running of the motor 48. Whilst the airscrew blades remain feathered the valve 33 remains in the lifted position. a

In order to prevent the return fluid from the hydraulic motor l5 passing into the engine as is the case during feathering with known arrangements, the following arrangement is provided. I A non-return valve 59 is provided in branch pipe-line 45 to prevent the return oil flowing'fr'om'the hydraulic motor i5 from flowing into pipe-line 2| and a return pipe 80 is connected to the branch pipe-line 45 between the non-return valve 59 and its point of connection to pipe-line 38 so that the return oil flows into return pipe and is delivered to the reservoir I3.

A relief valve 6| is provided in return pipe 60 and reservoir l8 through pipe-line 49 and delivers through pipe-line 50 comprising filter 5| and non-return valve 52 to valve 33 and thus to the hydraulic motor [5. The oil is taken from reservoir l8 as when feathering more rapid pitch changes occur, and thus more oil is required than when the constant speed governor is operating. The supply of current from a battery 53 to motor 48 is controlled by a switch 54. A feathering trip lever 51 is operated by manual selection to engage a shoulder 58 on an extension 33a of piston valve 33 to lift the valve 33 against spring 39, thereby to admit pressure fluid delivered by pump -41 to space I50 and to feather the airscrew blades I4a. Thus to feather the airscrew blades the the relief valve is loaded to open when the pressure in the pipe-line 45 is substantially higher than the normal delivery pressure in the lubricating system. If, for instance, valve 23 is loaded to open at 70 lbs/sq. in. the valve 6| may be loaded to open at lbs/sq. in. This arrangement prevents topping up oil flowing in the direction of arrow 46 from being returned directly to the reservoir l8. r I

The oil flows during feathering are indicated by chain line arrows 62.

To move the blades from the feathered position the lever 51 is operated to allow the valve 33 to drop and the switch 54 is again closed to supply pressure fluid to the hydraulic motor l5. Pressure fluid is thus delivered to space i517 and the blades Ma moved from the feathered position to a flne pitch setting suitable for starting. i

The feathering operation of the system is as follows:

During normal operation of the constant speed governor unit, the valve iii in the return pipe 60 to the tank is closed since the oil pressures developed in the return pipe line do not reach a value of 100 lbs. per square inch. Any losses of oil from the closed constant speed governor unit circuit are made up by oil flowing from the engine oil pump 20 past the non-return valve 59 in the branch pipe 45 and, since the delivery pressure of the engine oil pump is about 70 lbs. per square inch, no oil will flow back to the engine oil tank paslila the valve 6| set to open at 100 lbs. per square inc 1 During feathering and unfeathering, the return oil is prevented by the non-return valve 59 in the branch pipe 45 from being, delivered intto the engine and the pressure in the pipe line 45 builds up until it is suflicient to open the valve ii. in this way, during feathering and unfeathering operations under control of the feathering and unfeathering unit, 011 drawn from the engine oil tank by the pump 41 of the mechanism. is made up by return oil, and over-oiling of the engine prevented. I

The arrangement above described is especially useful when the airscrew is, as illustrated, driven from a gas-turbine engine as such engines have a. low oil capacity and a small sump capacity.

We claim:

1. For use with an engine arranged to drive a variable pitch airscrew, the combination with an engine lubricating system comprising a reservoir and an engine pressure oil conduit to deliver pressure oil to the engine, of a hydraulic constant speed governor unit comprising a pump, a-hyd li M v q srnq w s ss 'a e du from said pump to the hydraulic motor and a return oil conduit from said hydraulic motor to the suction side of said pump; of a branch conduit connected to said engine pressure oil conduit and to said return oil conduit; of a feathering and unfeathering unit comprising a second pump connected to withdraw oil from said reservoir and to deliver oil to said hydraulic motor through said governor pressure conduit, and an electric motor to drive said second pump; of a non-return valve in said branch conduit arranged to prevent oil flow from the return oil conduit to said engine pressure oil conduit; of a further conduit connected with said branch conduit between the nonreturn valve and the return oil conduit and arranged to deliver to the reservoir; and of a loaded valve in said further conduit arranged to open only when the pressure in said branch conduit reaches a selected value in excess of the pressure in the engine pressure oil conduit.

2. For use with an engine having a variable pitch airscrew, the combination with a circulatory engine oil pressure system, a, constant speed governor unit for controlling the airscrew pitch comprising a closed hydraulic circuit, a conduit connecting the closed hydraulic circuit with the circulatory engine oil pressure system to convey oil from the engine oil pressure system to the closed hydraulic circuit, and a feathering and un- 6 feathering hydraulic circuit for the airscrew, comprising a fluid reservoir and said conduit to convey return fluid of the feathering and unfeathering hydraulic circuit; of valve means connected in said conduit to prevent the return fluid of said feathering and unfeathering hydraulic circuit flowing into said engine oil pressure system, and means connected to convey said return fluid from said conduit to said reservoir and arranged to operate when the pressure of said return fluid in said conduit attains a selected value in excess of the pressure in said engine oil pressure circuit.

' LIONEL HAWORTH.

CHRISTOPHER LINLEY JOHNSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,186,791 Wilgoos Jan. 9, 1940 2,525,694 Lindsey et al Oct. 10, 1950 2,526,409 Price Oct. 17, 1950 FOREIGN PATENTS Number Country Date 550,533 Great Britain Jan. 13, 1943 

